An artery is one of the tube-shaped blood vessels that carries blood away from the heart to the body's tissues and organs. An artery is made up of an outer fibrous layer, a smooth muscle layer, a connecting tissue layer, and the inner lining cells. If arterial walls become hardened due to the accumulation of fatty substances, then blood flow can be diminished. Hardening of the arteries, or loss of vessel elasticity, is termed arteriosclerosis while fatty deposit build-up is termed atherosclerosis. Atherosclerosis and its complications are a major cause of death in the United States. Heart and brain diseases are often the direct result of this accumulation of fatty substances that impair the arteries' ability to nourish vital body organs.
The use of balloon catheters to treat stenosis or narrowing within various parts of the human body is well known. Balloon angioplasty is a nonsurgical method of clearing coronary and other arteries, blocked by atherosclerotic plaque, fibrous and fatty deposits on the walls of arteries. A catheter with a balloon-like tip is threaded up from the arm or groin through the artery until it reaches the blocked area. The balloon is then inflated, flattening the plaque and increasing the diameter of the blood vessel opening. The arterial passage is thus widened. As a result of enlarging the hardened plaque, cracks and lesions may unfortunately occur within the plaque to expose the underlying fresh tissue or denuded cells to the blood stream.
In one typical procedure, for example to dilate a stenotic region in a coronary artery, a relatively large guiding catheter is inserted into the patient's arterial system in the groin. The guiding catheter is then advanced through the arteries to a location near the patient's heart. A small wire guide is then inserted into the guiding catheter and advanced to the distal end of the guiding catheter, at which point it is steered to extend through the stenosis in the coronary arteries. A balloon catheter is then advanced over the wire guide until the deflated balloon lies across the stenosis. A working fluid is then pumped through the balloon catheter, thereby inflating the balloon and dilating the passage through the stenosis.
There are limitations, however, to this technique's application, depending on the extent of the disease, the blood flow through the artery, and the part of the anatomy and the particular vessels involved. Plaque build-up and/or severe re-stenosis recurs within 6 months is reportedly up to about 40 percent of those treated. Balloon angioplasty can only be characterized as a moderate-success procedure. Recently, a newer technique of inserting a metallic stenting element is used to permanently maintain the walls of the vessel treated at its extended opening state. Stents are tiny mesh tubes made of stainless steel or other metals and are used by heart surgeons to prop open the weak inner walls of diseased arteries. They are often used in conjunction with balloon angioplasty to prevent restenosis after the clogged arteries are treated. Stenting technique reduces the probability of restenosis; however, the success rate is still sub-optimal. The underlying fresh tissue or denuded cells still pose as a precursor for vessel spasms, reclosures or stenosis due to unknown reasons.
When a clogged artery is widened, the plaque is broken up and the underlying collagen or damaged endothelium is exposed to the blood flow. Collagen and/or damaged endothelium have a pro-thrombotic property that is part of body's healing processes. Unless the collagen or the damaged endothelium is passivated or modulated, the chance for blood vessel clotting as well as restenosis always exists. Moderate heat is known to tighten and shrink the collagen tissue as illustrated in U.S. Pat. No. 5,456,662 and U.S. Pat. No. 5,546,954. It is also clinically verified that thermal energy is capable of denaturing the tissue and modulating the collagenous molecules in such a way that treated tissue becomes more resilient ("The Next Wave in Minimally Invasive Surgery" MD&DI pp. 36-44, August 1998). Therefore, it becomes imperative to post-treat vessel walls after the walls are treated with angioplasty and/or stenting procedures.
One method of reducing the size of cellular tissues in situ has been used in the treatment of many diseases, or as an adjunct to surgical removal procedures. This method applies appropriate heat to the tissues, and causes them to shrink and tighten. It can be performed on a minimal invasive fashion, which is often less traumatic than surgical procedures and may be the only alternative method, wherein other procedures are unsafe or ineffective. Ablative treatment apparatus have an advantage because of the use of a therapeutic energy that is rapidly dissipated and reduced to a non-destructive level by conduction and convection, to other natural processes.
RF therapeutic protocol has been proven to be highly effective when used by electrophysiologists for the treatment of tachycardia; by neurosurgeons for the treatment of Parkinson's disease; and by neurosurgeons and anesthetists for other RF procedures such as Gasserian ganglionectomy for trigeminal neuralgia and percutaneous cervical cordotomy for intractable pains. Radiofrequency treatment, which exposes a patient to minimal side effects and risks, is generally performed after first locating the tissue sites for treatment. Radiofrequency energy, when coupled with a temperature control mechanism, can be supplied precisely to the electrode-to-tissue contact site to obtain the desired temperature for treating a tissue.
In the case of angioplasty alone, the enlarged blood vessel needs certain conductive tissue-contacting surface for delivering the RF thermal energy to the denuded collagen or damaged endothelium. A conductive elastomer electrode means can be coated or applied onto a rapid exchange balloon catheter or onto an over-the-wire balloon catheter, followed by connecting the conductive elastomer electrode means to a RF current source. It is useful in this case to shrink and tighten the target tissue through the conductive elastomer electrode means on the balloon surfaces by RF thermal therapy.
There is therefore a need in the prior art for a balloon catheter that may be used in association with a conductive elastomer electrode means on the balloon for angioplasty and tissue modulation purposes. The present invention is directed toward meeting this need for using the radiofrequency energy to treat a diseased artery or other tissues, such as esophagus, larynx, uterus, urethra and the like by a balloon means.